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Observational cosmology
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==Modern observations== Today, observational cosmology continues to test the predictions of theoretical cosmology and has led to the refinement of cosmological models. For example, the observational evidence for [[dark matter]] has heavily influenced theoretical modeling of [[structure formation|structure]] and [[galaxy formation]]. When trying to calibrate the Hubble diagram with accurate [[supernova]] [[standard candle]]s, observational evidence for [[dark energy]] was obtained in the late 1990s. These observations have been incorporated into a six-parameter framework known as the [[Lambda-CDM model]] which explains the evolution of the universe in terms of its constituent material. This model has subsequently been verified by detailed observations of the cosmic microwave background, especially through the [[WMAP]] experiment. Included here are the modern observational efforts that have directly influenced cosmology. ===Redshift surveys=== {{main|Redshift survey}} With the advent of automated [[telescope]]s and improvements in [[astronomical spectroscopy|spectroscopes]], a number of collaborations have been made to map the universe in [[redshift]] space. By combining redshift with angular position data, a redshift survey maps the 3D distribution of matter within a field of the sky. These observations are used to measure properties of the [[large-scale structure of the cosmos|large-scale structure]] of the universe. The [[Great Wall (astronomy)|Great Wall]], a vast [[supercluster]] of galaxies over 500 million [[light-year]]s wide, provides a dramatic example of a large-scale structure that redshift surveys can detect.<ref>{{citation|doi=10.1126/science.246.4932.897|pmid=17812575|title=Mapping the Universe|journal=Science|volume=246|issue=4932|pages=897β903|year=1989|last1=Geller|first1=M. J.|last2=Huchra|first2=J. P.|bibcode=1989Sci...246..897G|s2cid=31328798}}</ref> [[File:HSCSDMmap2018.gif|thumb|3D visualization of the dark matter distribution from the Hyper Suprime-Cam redshift survey on [[Subaru Telescope]] in 2018<ref>{{Cite web |last=Duffy |first=Jocelyn |date=October 2, 2018 |title=Hyper Suprime-Cam Survey Maps Dark Matter in the Universe |url=https://www.cmu.edu/news/stories/archives/2018/october/dark-matter-survey.html |archive-url=https://web.archive.org/web/20220412012749/https://www.cmu.edu/news/stories/archives/2018/october/dark-matter-survey.html |archive-date=April 12, 2022 |access-date=December 7, 2022 |website=Carnegie Mellon University}}</ref>]] The first redshift survey was the [[CfA Redshift Survey]], started in 1977 with the initial data collection completed in 1982.<ref>See the official CfA [http://cfa-www.harvard.edu/~huchra/zcat/ website] for more details.</ref> More recently, the [[2dF Galaxy Redshift Survey]] determined the large-scale structure of one section of the Universe, measuring ''z''-values for over 220,000 galaxies; data collection was completed in 2002, and the final [[data set]] was released 30 June 2003.<ref>{{Cite journal|doi=10.1111/j.1365-2966.2005.09318.x|title=The 2dF galaxy redshift survey: Power-spectrum analysis of the final dataset and cosmological implications|author=Shaun Cole|author2=et al. (The 2dFGRS Collaboration)|journal=Mon. Not. R. Astron. Soc.|volume=362|issue=2|pages=505–34|date=2005|doi-access=free |arxiv= astro-ph/0501174|bibcode = 2005MNRAS.362..505C |s2cid=6906627}} [http://msowww.anu.edu.au/2dFGRS/ 2dF Galaxy Redshift Survey homepage] {{Webarchive|url=https://web.archive.org/web/20070205010241/http://msowww.anu.edu.au/2dFGRS/ |date=2007-02-05 }}</ref> (In addition to mapping large-scale patterns of galaxies, 2dF established an upper limit on [[neutrino]] mass.) Another notable investigation, the [[Sloan Digital Sky Survey]] (SDSS), is ongoing {{As of|2011|lc=on}} and aims to obtain measurements on around 100 million objects.<ref>[http://www.sdss.org/ SDSS Homepage]</ref> SDSS has recorded redshifts for galaxies as high as 0.4, and has been involved in the detection of [[quasar]]s beyond ''z'' = 6. The [[DEEP2 Redshift Survey]] uses the [[Keck telescopes]] with the new "DEIMOS" [[spectrograph]]; a follow-up to the pilot program DEEP1, DEEP2 is designed to measure faint galaxies with redshifts 0.7 and above, and it is therefore planned to provide a complement to SDSS and 2dF.<ref>{{cite conference|title=Science objectives and early results of the DEEP2 redshift survey|author=Marc Davis|author2=et al. (DEEP2 collaboration)|date=2002|book-title=Conference on Astronomical Telescopes and Instrumentation, Waikoloa, Hawaii, 22β28 August 2002|arxiv=astro-ph/0209419}}</ref> ===Cosmic microwave background experiments=== {{main list|List of cosmic microwave background experiments}} {{excerpt|Cosmic microwave background#Discovery}} {{excerpt|Cosmic microwave background#Cosmic origin|hat=no}} {{excerpt|Cosmic microwave background#Progress on theory|hat=no}} {{excerpt|Cosmic microwave background#COBE|hat=no}} {{excerpt|Cosmic microwave background#Precision cosmology|hat=no}} {{excerpt|Cosmic microwave background#Observations after COBE|hat=no}} ===Telescope observations=== ====Radio==== The brightest sources of low-frequency radio emission (10 MHz and 100 GHz) are [[radio galaxy|radio galaxies]] which can be observed out to extremely high redshifts. These are subsets of the [[active galaxy|active galaxies]] that have extended features known as lobes and jets which extend away from the [[galactic nucleus]] distances on the order of [[megaparsec]]s. Because radio galaxies are so bright, astronomers have used them to probe extreme distances and early times in the evolution of the universe. ====Infrared==== Far [[infrared]] observations including [[submillimeter astronomy]] have revealed a number of sources at cosmological distances. With the exception of a few [[infrared window|atmospheric window]]s, most of infrared light is blocked by the atmosphere, so the observations generally take place from balloon or space-based instruments. Current observational experiments in the infrared include [[NICMOS]], the [[Cosmic Origins Spectrograph]], the [[Spitzer Space Telescope]], the [[Keck Interferometer]], the [[Stratospheric Observatory For Infrared Astronomy]], and the [[Herschel Space Observatory]]. The next large space telescope planned by NASA, the [[James Webb Space Telescope]] will also explore in the infrared. An additional infrared survey, the [[Two-Micron All Sky Survey]], has also been very useful in revealing the distribution of galaxies, similar to other optical surveys described below. ====Optical rays (visible to human eyes)==== Optical light is still the primary means by which astronomy occurs, and in the context of cosmology, this means observing distant galaxies and galaxy clusters in order to learn about the [[Large-scale structure of the universe|large scale structure]] of the Universe as well as [[galaxy evolution]]. [[Redshift survey]]s have been a common means by which this has been accomplished with some of the most famous including the [[2dF Galaxy Redshift Survey]], the [[Sloan Digital Sky Survey]], and the upcoming [[Large Synoptic Survey Telescope]]. These optical observations generally use either [[photometry (astronomy)|photometry]] or [[spectroscopy]] to measure the [[redshift]] of a galaxy and then, via [[Hubble's law]], determine its distance modulo redshift distortions due to [[peculiar velocities]]. Additionally, the position of the galaxies as seen on the sky in [[celestial coordinates]] can be used to gain information about the other two spatial dimensions. Very deep observations (which is to say sensitive to dim sources) are also useful tools in cosmology. The [[Hubble Deep Field]], [[Hubble Ultra Deep Field]], [[Hubble Extreme Deep Field]], and [[Hubble Deep Field South]] are all examples of this. ====Ultraviolet==== See [[Ultraviolet astronomy]]. ====X-rays==== See [[X-ray astronomy]]. ====Gamma-rays==== See [[Gamma-ray astronomy]]. ===Cosmic ray observations=== See [[Cosmic-ray observatory]].
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